Research &amp Scholarship

Observational Astronomer Explores Sources of Stellar Object Eruption

Stars can change brightness abruptly when undergoing explosive events such as a nova or supernova explosion. Although the brightest supernovas are visible up to 10 billion light years away, most stars beyond our galactic neighborhood are too faint to detect individually.

While many astronomical objects and phenomena last millions or billions of years, some are transient astronomical events, lasting just seconds to years.

Bahram Mobasher, a professor of physics and astronomy, is a member of a team of astronomers led by scientists at UC Berkeley and the University of South Carolina that reports the discovery by the Hubble Space Telescope of a transient stellar object with occasional eruptions during which its luminosity increases within a time of a few days or weeks.

The object is located behind the massive galaxy cluster MACS J0416.1, shown in the figure with the star-like object indicated by an arrow. Mobasher explained that the mass of this cluster curves space-time, acting as a lens, magnifying and distorting images of objects behind the cluster. The star-like object was discovered in January 2014 with a similar appearance in August of the same year.

The object is located behind the massive galaxy cluster MACS J0416.1, shown in the figure with the star-like object indicated by an arrow.

“It was amazing to catch a short-lived, very faint transient star right at the time its luminosity was increasing due to eruption,” said Mobasher, a coauthor on the Nature Astronomy paper reporting the discovery. “It is very important to find the nature of this process.” The paper reports not one but two transient events in a lensed galaxy behind a cluster which are more luminous than novae are normally, and faster and fainter than supernovae are.

The paper explores possibilities for the sources of these events and excludes common causes.

To examine whether the two transients originated from the same physical location in the source plane, Shoubaneh Hemmati, a former graduate student in Mobasher’s research group, looked for differences in the properties of the host galaxy at the location of each event.

“These peculiar transients are also interesting as they are very far compared to many previously found transients at these brightness levels,” said Hemmati, now a postdoctoral researcher at Caltech. “They were found because they are magnified by the lensing cluster in the field. The host galaxy of these two events is from the time the universe was about 5 billion years old. We estimated the stellar population of the host galaxy at different locations and found evidence of the two events being spatially coincident. The paper further finds that the two events are not likely to be temporally coincident.”

Such research can reveal not only the physical properties of the stars themselves, but more importantly the distribution of the dark matter — the material that cannot be directly observed but whose additional mass is thought to explain the observed internal motions of galaxies — in the lensing galaxy clusters.

– Iqbal Pittalwala

Expert on Magnetism Advances Knowledge of Spintronics Applications

Igor Barsukov, an assistant professor of physics and astronomy and a spintronics expert.

Igor Barsukov, an assistant professor of physics and astronomy and a spintronics expert, is a coauthor on a paper that appeared recently in Scientific Reports: “Oscillatory interlayer coupling in spin Hall systems.”

Multilayers of a few nanometer thickness play a central role in today’s spintronics research. Spin currents can be exchanged between magnetic and non-magnetic layers through buffer layers.

The collaborative team of UCR, UCI, and Brazilian researchers discovered a surprising and intricate spin interaction between the magnetic and non-magnetic layers, and studied its impact on multilayer magnetism.

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The University of California, Riverside (www.ucr.edu) is a doctoral research university, a living laboratory for groundbreaking exploration of issues critical to Inland Southern California, the state and communities around the world. Reflecting California's diverse culture, UCR's enrollment is now nearly 23,000 students. The campus opened a medical school in 2013 and has reached the heart of the Coachella Valley by way of the UCR Palm Desert Center. The campus has an annual statewide economic impact of more than $1 billion.